Fix yum package_method to be able to delete packages

The package_method yum from cfengine_stdlib.cf doesn't delete packages properly, because the package_name_convention is "$(name).$(version)", so you get a message like this:

```
rudder> Checking if package (tree,*,*) is at the desired state (installed=1,matched=1)
rudder>  -> Package promises to refer to itself as "tree.*" to the manager
rudder> !! Package name contians '*' -- perhaps a missing attribute (name/version/arch) should be specified
rudder>  -> Package version seems to match criteria
rudder>  -> Schedule package for deletion
```

Which ends up causing something like this:

```
rudder> Running /bin/rpm -e --nodeps tree.*  in shell
rudder> Executing /bin/rpm -e --nodeps tree.* ...
rudder> Q:rpm -e --nodeps tree ...:error: package tree.* is not installed
rudder> Q:rpm -e --nodeps tree ...:
rudder> !! Command related to promiser "tree" returned code defined as promise failed (1)
rudder>  ?> defining promise result class rpm_package_install_failed_tree
rudder> Bulk package schedule execution failed somewhere - unknown outcome for tree.*
```

This patch fixes that.